The present invention relates to a microcomputer suited to control industrial apparatus. More particularly, the invention relates to a microcomputer advantageously used for synchronization control.
Some types of equipment require synchronization controls such as an alternative current (AC) servo, a general-purpose inverter, and a programmable logic controller (PLC). Such industrial apparatus needs to control industrial motors by issuing specified instructions at specified time. A microcomputer is provided for the industrial apparatus and allows an inverter to control an industrial motor using an instruction that equals a pulse-width modulated (PWM) control signal. The pulse width is expressed in a duty, i.e., a percentage representing a ratio between High and Low periods. Industrial apparatuses may be simultaneously operated for a series of processes. In such a case, the microcomputer provided for each industrial apparatus controls the corresponding industrial motor. The industrial apparatuses need to synchronize the time (time synchronization) in order to consistently issue a sequence of instructions in a specified chronological order.
The synchronization accuracy required for the time synchronization between industrial apparatus rapidly tends to be strict. In some cases, the accuracy is required to be as high as a microsecond or shorter. Communication based on serial communication or proprietary communication has been used for the time synchronization between industrial apparatus. Recently, there is an increasing demand for synchronous Ethernet communication (hereinafter simply referred to as synchronous Ethernet) that appends a synchronization function to Ethernet (registered trademark). The synchronous Ethernet includes Ethernet/IP or Profinet based on the IEEE1588 standard and EtherCAT based on ring or daisy chain networks. The time synchronization accuracy tends to be stricter. Some synchronous Ethernet technologies compliant with the IEEE1588 standard enable the accuracy as high as a microsecond or shorter.
The industrial controller disclosed in patent document 1 includes multiple units coupled with each other each of which has a clocking function with an accuracy on the order of nanoseconds. Of these units, one functions as a master and the others as slaves. The adjustment means is provided to gradually approximate time axes for the slaves to the time axis for the master.
The technology disclosed in patent document 2 can synchronize execution of processing programs among networked controllers without adjusting timings. A timetable is preprogrammed for each controller to perform cooperative operations. Each controller includes a clock module to keep track of absolute time and a clock synchronization means to control the synchronization. If an event occurs to initiate a program, the controller broadcasts the time of the event occurrence as a trigger to the other controllers. A controller, when receiving the trigger, adds a specified delay time to the trigger to generate a delay trigger. The controller initiates a sequence of programs from the delay trigger.
The technology disclosed in patent document 3 ensures the time synchronization accuracy between a networked controller and devices. The master includes a master global timer. Each device includes a slave global timer and an operation cycle timer. The master transmits a packet containing a time stamp that is provided with the global time indicated by the master global timer. Each slave receives the packet to perform correction, namely, synchronize the operation cycle timer with cycle control using a cycle control synchronization timing indicated by the time stamp and a time difference indicated by the slave global timer.
The motion control system disclosed in patent document 4 enables synchronous operations according to ever-changing network load situations and is free from synchronization errors. The master monitors a communication delay and forces a slave to start operation for synchronization at the time that equals the current time plus the delay time.
The communication control system disclosed in patent document 5 provides multiple controllers each of which includes a communication controller and an actuator and manipulates control targets. The controllers are coupled via a network and can operate in synchronization with each other. The second embodiment provides a communication control system for time synchronization using the time synchronization protocol compliant with IEEE1588. The entire communication control system synchronizes the time. Then, the communication controller acquires communication delays from the controllers and adjusts the communication delays when transmitting control instructions to the controllers.
The data transmitter disclosed in patent document 6 changes image data being received to image data from other image information devices. The image information device includes a clock processing portion that generates the current time synchronized with the time information received from the network. The image information device changes the received data when detecting a match with the specified time received from the system controller via the network. This enables to change image data in synchronization with an image frame (I frame) even if a change request is input between an I frame allowing the change and the next I frame.